Heat exchangers having built-in heat exchange tubes are used in order to recover heat of exhaust gas produced during travel of a vehicle. More specifically, exhaust gas is caused to flow along the inner periphery of the heat exchange tubes while a medium is caused to flow along the outer periphery of the heat exchange tube, so that heat of the exhaust gas is recovered.
A heat exchange tube for a heat exchanger disclosed in Japanese Patent Application Laid-open Publication No. 2003-28586 is shown in FIG. 17A. In FIG. 17A, the heat exchange tube 110 used in the heat exchanger includes: a first case half 111 having a generally U shape as viewed in front elevation; a second case half 112 having a generally U shape as viewed in front elevation and having side edge portions superimposed on side edge portions of the first case half 111; and a fin accommodated in a tube defined by the first and second case halves 111 and 112. A distal end portion 110a of each of the side edge portions of the first case half 111 is bent slightly inward to extend along the inner periphery of the second case half 112.
As shown in FIG. 17B that is a fragmentary enlarged view of a section encircled at 17B in FIG. 17B. It is customary to weld together the first and second case halves 111 and 112 in order to prevent leakage of fluid from the tube. At the time of welding, a weld bead 116 is formed such that the first and second case halves 111 and 112 are welded together via the bead 116.
However, if the bead 116 protrudes beyond the outer surface of the first case half 111, then mountability of the heat exchange tube would be degraded. It may be conceivable to shave off the protruding portion of the bead 116a, in which case, however, the number of steps necessary for manufacturing the heat exchange tube 110 would increase and hence the number of steps necessary for manufacturing the heat exchanger would also increase.